Vapor filled thermionic tube



Jan. 8, 1935. w. w. EITEL ET AL 1,987,328

VAPOR FILLED THERMIONIC TUBE Filed May 27, 1953 INVENTORS.

WILL/AM W. E/TEL JACK McCULLOUGH.

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ATTORNEY Patented Jan. 8, 1935 i r 1,987,328

1,987,328 VAPOR FILLED THERMIONIC TUBE" William W. Eitel and Jack McCullough, San Bruno, Califi, assignors toIHeintz & Kaufman, Ltd., San Francisco, Calif., a corporation of Nevada Application May 27, 1933, Serial No. 673,234

- 6 Claims. (01. 250-27) Our invention relates to thermionic tubes havcient. Low anode voltages are desirable and relaing a control electrode, and more particularly to tively easy. to obtain, such tubes having a filling of conductive gas, and Considering devices having anode and cathode in which output currents are substantially of a alone, large reductions inresistance therebetween waveform corresponding to that of the input voltmay be obtainedby gas filling the tubes, with re:- 5

ages supplied to the o tr l le tr de, sultant and consequent lower anodevoltage, and

Among the objects of our invention are: To prolower anode resistance, due to ionization by 'imvide a gaseous filling in a thermionic tube while pact or collision, the space charge being "material retaining control of the output; to. provide a 1y reduced or entirely eliminated Electron dismeans for increasing the current flow through a arge devices of this kind are exemplified y 10 thermionic tube; to provide a highly efficient gas vapor filled rectifiers, particularly those E'of jthe filled amplifier and oscillator tube in which the u y V p yp The gaseous fi greatly de-ionization time of the gas is relatively unimadds to the life of the filament'or'cath'ode, parportant, and not detrimental to proper operation; ticularly when oxide coated heatableiconductors 15, to provide a gas filled thermionic tube having porare us das a cathode.

tions of differing pressure therein, and to utilize Such vapor filled tubes, however, are not subthese differences of pressure to provide a, more ject to electrostatic contr'olof. anodecurrent, as eflicient tube; to provide a means for preventing are purev electron discharge t b sp ha a positive ion sheath around a control electrode s absent, and a positive n Sheath forms around in a gas filled thermionic tube; to provide meththe Control e ctrode, these. factors p vent g 20 ods of controlling an ionized gas to produce am- Waveform amplification. 1 plification of electric currents, and the genera- Certain vapor tubes havebeendeveloped using tion of high frequency oscillations; and to proa yp ofx ontrol, which, however, is that. r of vide a simple, low impedance, high power ampliw t h n ra e a Wav m r production.

fier and oscillator tube, and method of generatn his typ of be'kn wn nd r'the tra -rname 25 ing a profuse number of electrons to be used in of T yrat t e a d urr n ay -started Such device by application of a positive potential to thegrid,

Other objects of ourinvention will be apparent but Which cannot b pp y g d influence or will be specifically pointed out in the descripaloneras a Sheath-formed from p v ions tion forming a part of this specification, but we P s n the oni d s/around the'grid struc- 30- do not limit ourselves to the embodiment of the ture effectivelyrrevents negative potential n: invention herein described, as various forms may plied t the, gridv afiectine anode fl wbe adopted within the scope of the claims. Such ev therefore, not pt 0.1

' In the drawing which illustrates one preferred used s amplifiers 0r c a on generators. V

' The device employing the methods and con,

UNITED STATES 'PATENTQOFFICE f 35 form of our invention embodying the methods described herein; StlllCtlOIl' of our invent on is gas filled, andderives Figure 1 is longitudinal sectional View of a from that filling theinherent advantages thereof. vertically positioned tube, and a diagram, sche- The anode fl maybe Pontmued, 190th Sta1ted matic and reduced to lowest terms, of a circuit and stcpped Substantlal yconformlty Wlth the 40 voltage applied to a control electrode. 40'

in which the device may be utilized.

.Figure 2 is a cross sectional view taken as in dicated by the line 22 in Figure 1.

In high power thermionic tubes of the pure Broadly considered, the-novel methods utilized by us to accomplish full grid control in a, vapor filled tube comprise one or'more of the stepsof creating a difference of vapor pressure within electron discharge type the cathode is the sole the device, providing a conductive path'between 45* source of electrons, and as such is subject to deportions of the gas having difierent pressures, terioration, particularly as high anode voltages ionizing the in e high pressure t bare customarily necessary due to relatively high stracting a Substantial, number of positive i n resistances between cathode and anode. In adfrom the path to leave a remainder composed u dition tolifelimitafion due tfi13mentaryimpairstantially of electrons, directing the electrons 50 merit and eventual breakdown, associated ppainto a low pressure'portion of the gas where fur-'v ratus necessary to produce the needed high anode ther ionization by-collision is negligible, and con-1 voltages, together with means to smooth the sup-, trolling and collecting the electrons in the low ply toa-substantially pure direct current, is highpressure portion; We also prefer, to make the 55. 1y expensive, cumbersomadangerous and mom-, controlling field subject togapotentiahgradient It is often preferable cathodeiand 'the-grid;

such as will tend to prevent the formation of a positive ion sheath around the end of the controlling field.

It has been stated that an envelope containing a condensable gas such as mercury in vapor phase, has a uniform pressure throughout corresponding to the vapor pressure of the coldest portion. Such a statement while generally correct is not specifically true, and does not apply to many envelopes wherein diiferences of pressure may be developed. An example, is the well known mercury vapor vacuum pump wherein mercury inliquid phasezis boiled in one portion of a container, cooled and condensed in another, thus; buildingup. pressure differences sufficient to cause.vaporucirculation, and consequent pumping action utilizing the injector principle. This general method of obtaining a pressure difference is used in our invention pressure between to create a difference in vapor the anode end and the cathode end of our envelopc;. We ellow the cathode? end to become heated, while cooling the anode end. The difference in. pressure may be regulated by the actual temperature. diflerence, :and practically all mercury vapor may berremoved from the anode end, if desiredgbyxcoolingin liquid air.

The. apparatus of our invention in broad terms maybe described asan envelope having therein tin-anode .at.one end,a cathode at the other, to provide apath therebetween- A'control electrode of grid is placed adjacent the anode between the anode and cathode. The tube isprovided with a gaseous filling'preferably mercury vapor. Means are provided for cooling the anode end of the envelope, the cathode preferably serving to heat the. cathode rend, although additional heating meansma'y be supplied.

when the anode is energized heavy ionization takes place around-the cathode, and means are provided between the cathode and the grid to abstract positive ions from the ionized portion. The remaining electrons pass into the cooled portionof the envelope, and, the mean free path of the gas particles being greater than at the heated I end,electrons'do not there cause any substantial ionization. Here they are acted on by the grid, and '-:collected bythe anode. The means for-collecting the ions is preferably -a screen surrounding the cathode andpath' to the grid, the screen being'connected toa source of negative potentiali Referring to'the drawing, a cylindrical envelope 1 is provided with a cathode stem 2 at one end,

through which cathode leads 4 are sealed. The

' l leads, extending 'irfto'theinterior of the envelope,

support a cathode 5', preferably-of oxide coated metallic ribbon. 1 posite end-o'f the envelope is provided withan electrode stem 6 through which is sealeda central 'anode lead land a grid lead 9. A dumm'y ih together with the grid lead 9 supportagridu of metal gauzel2 m'ounted on a ring 14*, placed between an anode 15 mounted on the anode lead '7, and the cathode. It' is preferaible that the g'rid '11 and the anode be relatively close, leavingl a relatively long path between the anode-gridassembly and'the cathode. Surroundingthe cathode andextend ing almost to the grid is'a mesh screen collector 'lfi'applied in the form of a cylinder to-' the inner walls of the envelope. to extend the collector to include the grid, and may if desired be shortened to avoid snrrounding the cathode; It should, however, be adjacent the portion of the path to beionizedjwhich is that portion between the A screen lead 1'7 is fastened to the screen collector, extended laterally and sealed through a side tube 19 to provide an electrical connection.

The device is then evacuated in accordance with known methods of pumping, a small quantity of mercury in liquid phase 20 is placed in the .tube, andwhen thoroughly freed from gases other than mercury vapor, is sealed from the pumps. Other gases capable of assuming liquid phase within the temperature range available may be used if desired.

Cooling means, in this case a cooling jacket 21 is then applied tothe upper portion of the envelope, surroundingthe anode and control electrode and extendingto a point above the cathode. Water or othercooling agents may be circulated through the jacket by use of the connections 22.

Figure 1 also shows diagrammatically a circuit inwhich the tube is operable. A cathode source 23 is connected to the cathode leads 4. A biasing source 2 is connected to one cathode lead and'to the screen lead 17 to place on the ,screena negative potential. An anode source 25 is connected through output posts 26*to the anode lead 7, and one ofthe cathode leads 4 is connected to the grid lead 9 through input posts 27.; As thetube is adapted to beused as either an amplifier'or' oscillator the remainder of the input and output circuits are not shown, as they will not difier from circuits well known in the art, and as such are no part of our invention.

In operation, the cathode is'heated, and cooling liquid circulated throughthe jacket; The heat ofthe cathode 'vaporizes' a portion of the mercury and the vapor pressure rises in thelower end of the envelopeadjacent the cathode. The cooling jacket however causes a condensation to-take place before the vapor can reach the anode end'of the tube; itbeing preferable to com pietely remove all mercury in liquid phase from the upper portion'of'the tube. A difference in pressure is'built up, the pressure being highest adjacent the cathode, and lowest adjacent the anode and control electrode.

In the tube referred to, 500 voltswas' impressed on the anodegfrom the anodetsource 25 through the proper circuit. The region around the cathode became highly ionized, the ionization decreasing toward the anode. 150' volts negative potential was'placed on the collector from the biasing source 24, and positive ions from the portion of the-path between thecathode and control electrode are attracted to the collector, leaving in addition to the electrons emitteddirectly from the cathode, those caused by impact in the ionized gas. The augmented stream of electrons passes onto thecontrol electrode through gas :haying a-longer mean free path, collision ionization becomes less and less, more ions are abstracted by the collector, .until. in the vicinity of the grid, the stream is substantially all electrons, with few ions. remaining. This stream passes through the meshes of the grid to the anode, and withother voltages as specified 20.volts negative on the grid will stop the stream, the stream immediately restarting upon removal of the negative charge. Positive grid voltages increase the-current to the anode and the characteristic control curve greatly resembles the usual curve of high vacuum tubes.

While it is possible in this manner to create a controllable low resistance path between cathode and anode which will 'be entirely free from ions in the vicinity of the control electrode and anode, weprefer -to utilize an additional feature to prevent a positive ion sheath from formingaround the control electrode. We may desire to extend the collector screen to a point closely adjacent the grid. We may in certain tubes enclose the grid as well as the cathode.

With volts negative on the screen and the grid at zero, the screen is 150 volts negative to the grid, tending to draw away from the grid all positive ions approaching it. At 20 volts negative on the grid the screen is still 130 volts negative to the grid, at 20 volts positive on the grid the screen is volts negative to it, so that at all times during the operation of the grid between 20 volts negative and 20 volts positive, there is a gradient between the grid and the screen tending to draw all positive ions approaching the grid to the screen, thus efiectively preventing the formation of a positive ion sheath on the grid.

The tube is an effective amplifier and oscillator at high frequencies, the anode resistance is exceedingly low due to the electrons caused by impact ionization, waveforms are not substantially distorted, and large power outputs have been obtained without excessive deterioration of the cathode, with low anode voltages.

We claim:

1. The method of controlling conduction through a body of gas which comprises the steps of ionizing a current path through said gas, creating a difierence of vapor pressure between the ends of said path, abstracting a substantial amount of ions from the high pressure end of said path and controlling the remainder of said current near the low pressure end of said path.

2. A vapor tube comprising an envelope, a filling of conductive gas in said envelope, a cathode and an anode adapted to ionize the gas adjacent said cathode when energized, a control electrode between said anode and cathode, means for preventing the formation of a positive ion sheath around said control electrode, and means for preventing ionization by collision between said control electrode and said anode.

3. A vapor tube comprising an envelope, a filling of conductive gas in said envelope, a cathode, an anode, a control electrode between said anode and cathode, means for ionizing the gas adjacent said cathode, means for preventing the formation of a positive ion sheath around said control electrode, and means for preventing substantial ionization between said control electrode and said anode.

4. A vapor tube comprising an envelope, at filling of conductive gas in said envelope, an anode, a cathode, a control electrode between said anode and said cathode, a conductive electrode surrounding at least a portion of the path between said cathode and said control electrode, means for establishing a potential gradient between said anode and said cathode sufiicient to ionize the gas adjacent said cathode, and means for establishing an opposite potential gradient between said cathode and said conductive electrode whereby a substantial number of positive ions are abstracted from said gas.

5. A vapor tube comprising an envelope, a filling of conductive gas in said envelope, an anode, a cathode, a control electrode between said anode and said cathode, a conductive electrode surrounding at least a portion of the path between said cathode and said control electrode, means for establishing a potential gradient between said anode and said cathode suflicient to ionize the gas adjacent said cathode, means for establishing an opposite potential gradient between said cathode and said conductive electrode whereby a substantial number of positive ions are abstracted from said gas, and means for establishing a potential gradient between said control electrode and said conductive electrode thereby preventing a positive ion sheath from forming around said control electrode.

6. A vapor tube comprising an envelope, a filling of conductive gas in said envelope, an anode, a cathode, a control electrode between said anode and said cathode, a conductive electrode surrounding at least a portion of the path between said cathode and said control electrode, means for establishing a potential gradient between said anode and said cathode sufficient to ionize the gas adjacent said cathode, means for establishing an opposite potential gradient between said cathode and said conductive electrode whereby a substantial number of positive ions are abstracted from said gas, means for establishing a potential gradient between said control electrode and said conductive electrode thereby preventing a positive ion sheath from forming aroimd said control electrode, and means for preventing substantial ionization between said control electrode and said anode.

WILLIAM W. EITEL. JACK MCCULLOUGH. 

